The present invention relates to a magnetic recording medium, particularly a magnetic recording tape, comprising a base film, a magnetic layer provided on one surface (i.e. the major surface) of the base film and a back coat layer provided on the other surface (i.e. the back surface) of the base film.
A magnetic recording tape comprises a base film and a magnetic layer provided on the flat surface (i.e. the major surface) of the base film, the surface of the magnetic layer being finished to be flat. When the surfaces of the base film are too flat, the coefficient of friction between the back surface of the base film and the guide part at the passage of the magnetic recording tape is substantially increased. As a result, the running stability of the magnetic recording tape is deteriorated, and the normal recording and reproducing of signals is made difficult. In order to overcome this drawback as described above, a layer comprising non-magnetic particles is provided on the back surface of the base film to make a roughened surface. When, however, the back coat layer has an excessively roughened surface, the roughening is transferred to the surface of the magnetic layer when the tape is in a wound state and the magnetic characteristics deteriorate. Further, when the abrasion resistance of the back coat layer is too low, the nonmagnetic particles therein are readily removed and adhere onto the surface of the magnetic layer. This also deteriorates the magnetic characteristics. Furthermore, when the back coat layer is too hard, serious abrasion occurs at the parts (e.g. the tape guide) of the recording and reproducing apparatus on which the back coat layer runs in close contact.
Various proposals have been made with respect to the materials for a back coat layer, especially the kind and size of the non-magnetic particles to be included in the back coat layer. However, those proposals have failed to produce a back coat layer which is satisfactory so as to assure high running stability and good magnetic characteristics without causing any serious abrasion to that part of the apparatus on which the back coat layer runs in close contact.
As a result of extensive study, it has been found that the use of certain specific inorganic pigments as the non-magnetic particles for formation of a back coat layer can provide a magnetic recording tape having satisfactory running stability and magnetic characteristics without causing any substantial abrasion problem. The property of a substance which prevents any substantial abrasion to any other material will be hereinafter referred to as a "non-abrading property".